prop advice

[betty boop]

first of many questions on the new boat.

she has an alpha 1 G2 leg on the 4.3L merc but I had a minor ding to the prop on the Thames last week so it needs a repair. I put on the SS laser 2 I hve from Betty and its making a terrible vibration and fuel economy is thru the floor (may be related).

Are all props for the Alpha drive the same or do I need one to match the boat / engine / gear ratio?

the SS prop was fine when tested at the IOW festival on the 3.0l engine so I doubt its damaged, I don't really want to repair the Ali original prop just to prove its OK then buy a new SS prop so thought Id cut out the middle man esp as its covered in Anti foul as well as damaged.

Symptoms on the SS prop, low speed vibration/shudder, bad fuel economy, long time to drag on the plane and a terrible listing to port. Any of these could be other faults as she's only been tested at 5-8mph before and had none of them.

[Bigplumbs]

Can you give us a bit more info on the sizes of props etc. Also stupid question but did you put the spacer/front bit on correctly.

Dennis

[BruceK]

There is not enough info to diagnose your problem but one thing can be said in confidence

Are all props for the Alpha drive the same or do I need one to match the boat / engine / gear ratio?

No, not all props are the same, yes you do need to match.

A consistent lean to port having changed prop or damaged prop has a likely cause of the prop not cutting the water cleanly and causing an exaggerated torque effect. Either too coarse or damage to the pitch. If so it would be most prominent under load coming out of the hole.

Vibration, shudder etc could be a myriad of problems. Start eliminating them piecemeal beginning with a new prop. Firstly I love stainless steel props, but really they are a daft idea. They will accelerate galvanic corrosion, they are too strong and will transfer any propstrike into the gearbox and cause massive damage to the gearbox if the strike has enough impetus behind it. (I've destroyed 3 boxes in 2 years). They are horrendously expensive by comparison. My advice is forget the bling and go ali. Match it to your boat.

[betty boop]

not sure I can give more info on the porp size, the SS Lazer sould be marked so I'll look at that one but the Ali is in a bit of a state with anti foul barnicles etc. so no markings & first attempts at ordering a new one met with a miriad of size options I have no idea on But good point on the collars/spacers, YES I am sure they are on correctly but we were very rushed launching when i put it on and it is a different sleeve set up, the original having all the spacers and hubs mounted on the prop, the SS having individual parts but as I remove the prop on BB every trip out Im sure I got it right this time. may be.

99.999999% sure the crunch hasnt damaged anything but the blade tips, a crunch on gravel and a steel slipway frame at 800 RPM just as we came in to moor up, I blame the 1st mate for being on the phone at the time.

Not a fan of Ali props so I'll avoid them to be honest, we use her on shallow rivers and I've lost too many blade tips on the river bed, the SS prop is/was a preffered on the lower Thames and we've just gone on from there with them, they are heavy though for sea use esp when carrying a full boat load. If you've lost gear boxes from SS props Im assuming you didnt have the break away spline set up thats on the collar these days? I hit a rock in Poole some time ago although I took a chunk from the skeg and lost 2 blades, the splines broke and the gearbox spun freely with no damage. was a life (wallet) saver in that instance.

back on topic though where do I get the correct spec for a new prop?

[Ianfs]

Which plugs have you got in the vent holes?

[BruceK]

I most certainly did. Did it help? Did it heck

[ColinR]

Worth contacting Steel Developments re matching prop to boat.

http://www.steeldevelopments.net/

[Ianfs]

I've got a spare Ali 19" pitch if that helps. I'm not sure if it'll fit the Gen 2 though.

[Overfinch]

Alpha 1 and bravo 1 drive props are same both 13 spline. Prop is likely cause of your issues but as others have said there are many other potential causes.
More info is needed ie WOT rpm with current set up, pitch of prop and drive ratio.
As you can not provide this due to your issues my best guess is that you have 1.81 ratio, heavy ish boat 1600kg? Rpm range 4600-5000? 19 pitch x 14 1/4 3 blade would not be far out. SS props can be re-pitched by 1 degree Ali by 2. You are likely to go through 2 or 3 to get the right one. What we need is a prop swap shop on here! I have half a dozen but have learnt a lot in the process. The main one being that it's a black art, resist temptation to alter too many variables ie number of blades, big blades etc. Get a 3 blade for a baseline and go from there.

[shibbs]

All very interesting this. I have too had the same issues trying to get my WOT revs as i would expect it to be. So far, i have found a high 5 19p to be the best but still 1400rpm short of what it should be.

As for a prop swap shop - yes your right.

Speaking of which, i have a number of different props if anyone needs to try?

I have also just got hold of a four blade , a Trophy plus 19p, but i do not know if this is suitable for a Alpha 1? anyone got any ideas?

As for the original post, if none of these symptoms were present on the original prop, i would definitely try a different one, at least that can then point towards or eliminate it?

Let me know if you need to try one and we can arrange getting it to you?